Method of preparing viscose rayon



Uite tates Patent METHOD 0F PREPARING VISCOSE RAYON Marion Lytton, WestChester, Pa., assignor to American Viscose Corporation, Philadelphia,Pa., a corporation of Delaware No Drawing. Original application Dec. 30,1954, Ser. No. 478,940, now Patent No. 2,898,182, dated Aug. 4, 1959.Divided and this application Nov. 25, 1958, Ser. No. 776,204

4 Claims. (Cl. 106-165) This invention relates to the production ofshaped bodies of regenerated cellulose from viscose and moreparticularly to filaments and fibers of regenerated cellulose fromviscose.

In the conventional methods of producing shaped bodies of regeneratedcellulose from viscose, a suitable cellulosic material such as purifiedcotton linters, wood pulp, mixtures thereof, and the like is firstconverted to an alkali cellulose by treatment with a caustic sodasolution and after shredding the treated cellulose material, it isallowed to age. The aged alkali cellulose is then converted to axanthate by treatment with carbon disulfide. The cellulose xanthate issubsequently dissolved in a caustic soda solution in an amountcalculated to provide a viscose of the desired cellulose and alkalicontent. After filtration, the viscose solution is allowed to ripen andis subsequently extruded through a shaped orifice into a suitablecoagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscosesolution is extruded through a spinneret into a coagulating andregenerating bath consisting of an aqueous acid solution containing zincsulfate. The filament may subsequently be passed through a hot aqueousbath where it is stretched to improve its properties such as tensilestrength. The filament may then be passed through a dilute aqueoussolution of sulfuric acid and sodium sulfate to complete theregeneration of the cellulose, in case it is not completely regeneratedupon leaving the stretching stage. The filament is subsequentlysubjected to washing, purification, bleaching, possibly other treatingoperations and drying, being collected either before or after thesetreatments.

The filaments as formed by the conventional methods, consist of a skinor outer shell portion and a core portion with a sharp line ofdemarcation between the two. The cross-section of the filaments exhibitsa very irregular or crenulated exterior surface when even small amountsof zinc salts or certain other polyvalent metal salts are present in thespinning bath. The skin and core portions of the filament representdifferences in structure and these different portions possess differentswelling and staining characteristics, the latter permitting a readyidentification of skin and core. The sharply irregular and crenulatedsurface structure has a relatively low abrasion resistance and readilypicks up foreign particles such as dirt. Although the core portionposseses a relatively high tensile strength, it has a low abrasionresistance and a low flex-life, is subject to fibrillation and isrelatively stiff.

It has now been discovered that the presence of small amounts of certainalkali-soluble alkylene oxide adducts of N-fatty alkyl alanine(aminopropionic acid) in viscose results in the production of shapedbodies of regenerated cellulose such as filaments, films, sheets and thelike composed of all skin and having improved properties andcharacteristics providing that the amount of the alkylene oxide adductis maintained with certain limits and the 2 composition of the spinningbath is maintained within certain composition limits which will bedefined hereinafter. The most readily distinguishable characteristics ascompared to conventional filaments include a smooth, non-crenulatedsurface and the filaments consist entirely of skin.

The alkylene oxide adduct utilized in the modification of the viscosemay be an adduct of either the alpha or beta forms of N-fatty alkylalanine. The fatty alkyl group or radical is a straight hydrocarbonchain containing from 6 to 24 carbon atoms and may be saturated orunsaturated. The radical may be obtained from the fatty acids derivedfrom animal and vegetable fats and oils such as coconut oil, cottonseedoil, corn oil, soya bean oil, palm oils, peanut oil, tallow and the likeand the hydrogenated fats and oils. The N-fatty alkyl alanine asutilized for the purposes of this invention may be a pure compoundwherein a relatively pure fatty alkyl radical, such as a lauryl radical,is employed in preparing the adduct, or the N-fatty alkyl alaninemayconsist of a mixture of compounds where the fatty alkyl radicals areobtained from a mixture of fatty acids of a particular fat oroil such ascoconut oil. The adducts may be prepared by reacting a N-fatty alkylalanine, or a mixture of N-fatty alkyl alanines with an alkylene oxideor a polyoxyalkylene glycol. Adducts which are satisfactory for thepurposes of this invention may be derived from capric, lauric, myristic,oleic, stearic acids and like acids or from a mixture of fatty acidssuch as obtained from coconut oil or other fat or oil. The compounds maybe conveniently added to viscose in the form of solutions in alkali orin water.

This invention contemplates the use of alkylene oxide adducts of N-fattyalkyl alanines having from about 8 to about 30 or more alkylene oxideunits per molecule, preferably between about 12 and 20 alkylene oxideunits per molecule of the N-fatty alkyl alanine. It is obvious that forall practical purposes considering cost, ease of preparation, commercialavailability and solubility in water and in alkali solutions, theethylene oxide adducts are preferred. For purposes of illustration only,the invention is described by reference to'the ethylene oxide adductsbut it is to be understood that other alkylene oxide adducts such aspropylene oxide adducts are equally satisfactory so long as they possessthe required solubility. That is, the adduct must have suflicientsolubility to permit a minimum amount of the adduct to be dissolved inthe viscose. Commercial materials of this type such as the substancemarketed as Good-Rite CEA are entirely satisfactory. This substance isan ethylene oxide adduct of a mixture of N-fatty alkyl alanines whereinthe fatty alkyl radicals are obtained from coconut oil and have anaverage of about 15 ethylene oxide units per molecule of the N-fa'ttyalkyl alanine.

The amountof the adduct or modifier which is incorporated in the viscosemust be at least about 0.5% by weight of the cellulose in the viscoseand may vary up to about 4%, preferably, the amount varies from 0.5% to2.5%. V tion of products consisting entirely of skin and greater amountsaffect adversely the physical properties of the. products. Amountswithin the preferred range are most; effective in enhancing thecharacteristics and properties.

of the products. The adduct may be added at any desired stage in theproduction of the viscose such as in the preparation of the refined woodpulp for the manufacture of viscose, before or during the shredding ofthe alkali cel-- lulose, to the xanthated cellulose while it is beingdis solved in the caustic solution or to the viscose solution before orafter filtration. The adduct is preferably added Lesser amounts do notresult in the produce,

after the cellulose xanthate has been dissolved in the caustic solutionand prior to filtration.

The viscose may contain from about 6% to about 8% cellulose, theparticular source of the cellulose being selected for the ultimate useof the regenerated cellulose product. The caustic soda content may befrom about 4% to about 8%. and the carbon disulfide content may be fromabout 30% to about 50% based upon the weight of the cellulose. Themodified viscose, that is, a viscose containing. the small amount of analkylene oxide adduct of a N-fatty alkyl alanine may have a salt testabove about 7 and preferably above about 9 at the time of spinning orextrusion.

In order to obtain the improvements enumerated hereinbefore, it isessential that the composition of the spinning bath be maintained withina well defined range. The presence of the .alkylene oxide adduct in theviscose combined with these limited spinning baths results in the.production of yarns of improved properties such as high tenacity, highabrasion resistance, high fatigue resistance and consisting of filamentscomposed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is alow acid-high zinc spinning bath containing from about 10% to about 25%sodium sulfate and from about 3% to about 15% zinc sulfate, preferablyfrom 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Othermetal sulfates such as iron, manganese, nickel and the like may bepresent and may replace some of the zinc sulfate. The temperature of thespinning bath may vary from about 25 C. to about 80 C., preferablybetween about 45 C. and about 70 C. In the production of the all skintype filaments, the temperature of the spinning bath is not critical,however, as is well known in the conventional practice in the art,certain of the physical properties such as tensile strength varydirectly with the temperature of the spinning bath. Thus, in theproduction of filaments for tire cord purposes in accordance with themethod of this invention, the spinning bath is preferably maintained ata temperature between about 55 C. and 65 C. so as to obtain the desiredhigh tensile strength.

The acid content of the spinning bath is balanced against thecomposition of the viscose. The lower limit of the acid concentration,as is Well known in the art, is just above the slubbing point, that is,the concentration at which small slubs of uncoagulated viscose appear inthe strand as it leaves the spinning bath. For commercial operations,the acid concentration of the spinning bath is generally maintainedabout 0.4% to 0.5% above the slubbing point. For any specific viscosecomposition, the acidconcentration of the spinning bath must bemaintained above the slubbing point and below the point at which theneutralization of the caustic of the viscose is sufficiently rapid toform a filament having a skin and core.

There is a maximum acid concentration for any specific viscosecomposition beyond which the neutralization is suificiently rapid toproduce filaments having a skin and core. For example, in general, theacid concentration of the spinning baths which are satisfactory for theproduction of the all skin products from a 7% cellulose, 6%caustic-viscose and containing the alkylene oxide adducts lies betweenabout and about 8%. The acid concentration may be increased as theamount of the derivative is increased and also as the salt test of theviscose is increased. There is an upper limit, however, for the acidconcentration based upon the amount of adduct and the concentration ofcaustic in the viscose. All skin products cannot be obtained if the acidconcentration is increased above the maximum value although the amountofthe alkylene oxide adduct is increased beyond about 4% while otherconditions are maintained constant. Increasing the caustic soda contentof the viscose beyond about 8% is uneconomical for commercial productionmethods. For example, a viscose containing about 7% cellulose, about 6%caustic soda, about 41% (based on the weight of cellulose) carbondisulfide, and 2% (based on the weight of cellulose) of an ethyleneoxide adduct of N-fatty alkyl alanine, as described, in which the fattyalkyl radicals are obtained from the fatty acids of coconut oil andhaving about 15 ethylene oxide units per molecule, and having a salttest of about 9.5 when extruded into spinning baths containing 16 to 20%sodium sulfate, 4 to 8% Zinc sulfate and sulfuric acid not more thanabout 8% results in the production of all skin filaments. Lesser amountsof sulfuric acid may be employed. Greater amounts of sulfuric acidresult in the production of products having skin and core. A lowerin ofthe amount of the adduct, the lowering of the caustic soda content orthe lowering of the salt test of the viscose reduces the maximumpermissible acid concentration for the production of all skin filaments.It has been determined that the maximum concentration of acid which ispermissible for the production of all skin products is about 8.5%.

The presence of the adducts in the viscose retards the coagulation and,therefore, the amount of adduct employed must be reduced at highspinning speeds. Thus, for optimum physical characteristics of an allskin yarn formed from a viscose as above and at a spinning speed ofabout 50 meters per minute, the adduct is employed in amounts within thelower portion of the range, for example, about 0.6% to 0.75%. Thedetermination of the specific maximum and optimum concentration of acidfor any specific viscose, spinning bath and spinning speed is a matterof simple experimentation for those skilled in the art. The extrudedviscose must, of course, be immersed or maintained in the spinning bathfor a period sufiicient to effect relatively complete coagulation of theviscose, that is, the coagulation must be sufiicient so that thefilaments will not adhere to each other as they are brought together andwithdrawn from the bath.

In the production of filaments for such purposes as the fabrication oftire cord, the filaments are preferably stretched after removal from theinitial coagulating and regenerating bath. From the initial spinningbath, the filaments may be passed through a hot aqueous bath which mayconsist of hot water or a dilute acid solution and may be stretched fromabout 70% to about 120%, preferably between and Yarns for other textilepurposes may be stretched as low as 20%. The precise amount ofstretching will be dependent upon the desired tenacity and otherproperties and the specific type of product being produced. If desired,the filaments may be stretched in air. It is to be understood that theinvention is not restricted to the production of filaments and yarns butit is also applicable to other shaped bodies such as sheets, films,tubes and the like. The filaments may then be passed through a finalregenerating bath which may contain from about 1% to about 5% sulfuricacid and from about 1% to about 5% sodium sulfate with or without smallamounts of zinc sulfate if regeneration has not previously beencompleted.

The treatment following the final regenerating bath, or the stretchingoperation where regeneration has been completed, may consist of awashing step, a desulfurizing step, the application of a finishing orplasticizing material and drying before or after collecting, or mayinclude other desired and conventional steps such as bleaching and thelike. The treatment after regeneration will be dictated by the specifictype of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing thesmall amounts of the alkylene oxide adducts and spun in the spinningbaths of limited acid content have a smooth or non-crenulated surfaceand consist substantially entirely of skin. Because of the uniformity ofstructure throughout the filament, the swelling and stainingcharacteristics are uniform throughout the cross-section of thefilament. Filaments produced pursuant to this invention and consistingentirely of skin have a high toughness and a greater flexing life thanfilaments as produced according to prior methods which may be attributedby the uniformity in skin structure throughout the filament. Althoughthe twisting of conventional filaments, as in the production of tirecord, results in an appreciable loss of tensile strength, there isappreciably less loss in tensile strength in the production of twistedcords from the filaments consisting entirely of skin. Filaments preparedfrom viscose containing the alkylene oxide adducts have a high tensilestrength as compared to normal regenerated cellulose filaments, havesuperior abrasion and fatigue resistance characteristics and have a highflex-life. Such filaments are highly satisfactory for the production ofcords for the reinforcement of rubber products such as pneumatic tirecasings, but the filaments are not restricted to such uses and may beused for other textile applications.

The invention may be illustrated by reference to the preparation ofregenerated cellulose filaments from a viscose containing about 7.4%cellulose, about 6.3% caustic soda, and having a total carbon disulfidecontent of about 41% based on the weight of the cellulose. The viscosesolutions were prepared by xanthating alkali cellulose by theintroduction of 36% carbon disulfide based on the weight of thecellulose and churning for about 2% hours. The cellulose xanthate wasthen dissolved in caustic soda solution. An additional 5% carbondisulfide was then added to the mixer and the mass mixed for about onehour. The desired amount of the ethylene oxide adduct of N-fatty alkylalanine was added to the solution and mixed for about /2 hour. Theviscose was then allowed to ripen for about 30 hours at 18 C.

Example 1 Approximately 1% (based on the weight of the cellulose) of anethylene oxide adduct of N-fatty alkyl alanine (fatty alkyl groups fromcoconut oil) known as Good- Rite CEA was added to and incorporated inthe viscose as described above. The viscose employed in the spinning offilaments had a salt test of 9.4. The viscose was extruded through aspinneret to form a 208 denier, 120 filament yarn at a rate of about 22meters per minute. The coagulating and regenerating bath was maintainedat a temperature of about 60 C. and contained 7.8% sulfuric acid, 8%zinc sulfate and 17% sodium sulfate. The yarn was stretched about 82%while passing through a hot water bath at 95 C. The yarn was collectedin a spinning box, washed free of acids and salts and dried.

The individual filaments have a smooth, non-crenulated exterior surfaceand consist entirely of skin, no core being detectable at highmagnification (e.g. 1500X). The filaments of a control yarn spun withthe same viscose but without the addition of the modified agent and spununder the same conditions, exhibit a very irregular and serrated surfaceand are composed of about 85% skin and the balance core with a sharpline of demarcation between the skin and core. Other physical propertiesare set forth in the table which follows the examples.

Example 2 To a viscose as described above, there was added 2% of thesame ethylene oxide adduct (Good-Rite CEA). The viscose had a salt testof 9.4 and was spun into a 202 denier, 120 filament yarn by extrusioninto a spinning bath containing 7.8% sulfuric acid, 8% zinc sulfate and17% sodium sulfate. The bath was maintained at 60 C. and the extrusionrate was about 43 meters per minute. The filaments were subsequentlypassed through a hot water bath at 95 C. and stretched about 74%. Theyarn was collected in a spinning box, washed free of acids and salts anddried.

The individual filaments were readily distinguishable from controlfilaments in that they have a smooth, noncrenulated surface and consistentirely of skin while the control filaments have a very irregular andserrated surface and consist of about skin and the balance core with asharp line of demarcation between the skin and core. Other physicalproperties are set forth in the table which follows the examples.

Example 3 filament yarn by extrusion into a bath containing 7.4%

sulfuric acid, 8% zinc sulfate and 17% sodium sulfate. The bath wasmaintained at a temperature of 60 C. The extrusion rate was about 22meters per minute. The water bath was maintained at about 95 C. and thefilaments were stretched approximately 82% while passing through the hotwater. The yarn was collected in a spinning box, washed free of acid andsalts and dried.

The individualfilaments were readily distinguishable from controlfilaments prepared from viscose containing no modifier in that they havea smooth, non-crenulated surface and consist entirely of skin. Controlfilaments have a very irregular and serrated surface and consist ofabout 85 skin and the balance core with a sharp line of demarcationbetween the skin and core. Other physical properties are set forth inthe table which follows the examples.

Example 4 As a control for the foregoing examples, a viscose solution,prepared as described above, having a salt test of 9.7 was spun into a210 denier, 120 filament yarn by extrusion into a bath containing 7.5%sulfuric acid, 8% zinc sulfate and 19% sodium sulfate. The bath wasmaintained at a temperature of about 60 C. The extrusion rate was about22 meters per minute. The water bath was maintained at a temperature ofabout C. and the filaments were stretched 82% while passing through thehot water. The yarn was collected in a spinning box, washed free of acidand salts and dried.

The individual filaments have a very irregular and serrated surface andconsist of about 85 skin and the balance core with a sharp line ofdemarcation between the skin and the core. Other characteristics are setforth in the table which follows:

Although the tenacity and elongation are the only properties set forth,they have been chosen because of the ease and simplicity with which suchproperties may be determined. In some instances, products made inaccordance with this invention do not exhibit improvements in tenacityand elongation, however, the products consist of a smooth-surfaced, allskin structure and possess improved abrasion resistance, flex-life andother properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is itsrelatively high cross-sectional swelling when wet with water, thisswelling amounting to from about 65% to about 80% for rayon produced byconventional methods. Rayon filaments produced in accordance with themethod of this invention have an appreciably lower cross-sectionalswelling characteristic,

the swelling amounting to from about 45% to about 60%.

The alkylene oxide adducts may be added to any desired viscose such asthose normally used in industry, the specific Viscose composition setforth above being merely for illustrative purposes. The adducts may beadded at any desired stage in the production of the viscose and may bepresent in the cellulosic raw material although it may be necessary toadjust the amount present to produce a viscose having the properproportions of the adduct at the time of spinning.

The term skin is employed to designate that portion of regeneratedcellulose filaments which is permanently stained or dyed by thefollowing procedure: A microtome section of one or more of the filamentsmounted in a wax block is taken and mounted on a slide with Meyersalbumin fixative. After dewaxing in xylene, the section is placed insuccessive baths of 60% and 30% alcohol for a few moments each, and itis then stained in 2% aqueous solution of Victoria Blue BS cone.(General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entiresection is blue. By rinsing the section first in distilled water andthen in one or more baths composed of 10% water and 90% dioxane for aperiod varying from 5 to 30 minutes depending on the particularfilament, the dye is entirely removed from the core, leaving itrestricted to the skin areas.

This application is a division of my copending application Serial No.478,940, filed December 30, 1954,- entitled Method of Preparing ViscoseRayon, now Patent No. 2,898,182, dated August 4, 1959.

While preferred embodiments of the invention have been disclosed, thedescription is intended to be illustrative and it is to be understoodthat changes and variations may be made without departing from thespirit and scope of the invention as defined by the appended claims.

I claim:

1. A viscose spinning solution containing a small amount of a modifierselected from the group consisting of alkylene oxide adducts of N-fattyalkyl alanines and mixtures thereof, the fatty alkyl group being astraight hydrocarbon chain containing from 6 to 24 carbon atoms, thealkylene oxide being selected from the group consisting of ethyleneoxide and propylene oxide, the adducts containing at least 8 alkyleneoxide units per molecule of N-fatty alkyl alanine, said small amount ofthe; modifier being a quantity sufficient to impart a smooth,noncrenulated surface and a substantially all skin structure to productsformed by spinning the viscose at a sodium chloride salt test of atleast 7 into an aqueous bath containing from 15% to 22% sodium sulfate,from 4% to 9% zinc sulfate and sulfuric acid in an amount not exceeding8.5%, but the quantity being insufficient to adversely'affect thephysical properties of such products.

2*. A viscose spinning solution containing from about 0.5% to about 4%,based on the Weight of the cellulose in theviscose of a modifierselected from the group consisting of alkylene oxide adducts of N-fattyalkyl alanines and mixtures thereof, the fatty alkyl group being astraight hydrocarbon chain containing from 6 to 24 carbon atoms, thealkylene oxide being selected from the group consisting of ethyleneoxide and propylene oxide, the adducts containing at least about 8alkylene oxide units per molecule of N-fatty alkyl alanine.

3. A viscose spinning solution as defined in claim 2 wherein thealkylene oxide adduct is an ethylene oxide adduct as defined in claim 2.

4. A viscose spinning solution as defined in claim 2 wherein theselected modifier is a mixture of ethylene oxide adducts of N-fattyalkyl alanines, as defined in claim 2, in which the individual fattyalkyl radicals represent the fatty alkyl radicals derived from the fattyacids of coconut oil.

References Cited in the file of this patent UNITED STATES PATENTS

1. A VISCOSE SPINNING SOLUTION CONTAINING A SMALL AMOUNT OF A MODIFIERSELECTED FROM THE GROUP CONSISTING OF ALKYLENE OXIDE ADDUCTS OF N-FATTYALKYL ALANINE AND MIXTURES THEREOF, THE FATTY ALKYL GROUP BEING ASTRAIGHT HYDROCARBON CHAIN CONTAINING FORM 6 TO 24 CARBON ATOMS, THEALKLENE OXIDE BEING SELECTED FROM THE GROUP CONSISTING OF ETHYLENE OXIDEAND PROPYLENE OXJIDE, THE ADDUCTS CONTAINING AT LEAST 8 ALKYLENE OXIDEUNITS PER MOLECULE OF N-FATTY ALKYL ALANINE, SAID SMALL AMOUNT OF THEMODIFIER BEING A QUANTITY SUFFICIENT TO IMPART A SMOOTH, NONCRENULATEDSURFACE AND A SUBSTANTIALLY ALL SKIN STRUCTURE TO PRODUCTS FROMED BYSPINNING THE VISCOSE AT A SODIUM CHLORIDE SALT TEST OF AT LEAST 7 INTOAN AQUEOUS BATH CONTAINING FROM 15% TO 22% SODIUM SULFATE, FROM 4% TO 9%ZINC SULFATE AND SULFURIC ACID IN AN AMOUNT NOT EXCEEDING 8.5%, BUT THEQUANTITY BEING INSUFFICIENT TO ADVERSELY AFFECT THE PHYSICAL PROPERTIESOF SUCH PRODUCTS.